Flash Flood Warning 1, NWS Honolulu, HI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
805 PM HST WED DEC 31 2008

.SYNOPSIS...
A WEAK HIGH PRESSURE RIDGE NORTH OF THE STATE WILL KEEP WINDS
LIGHT TONIGHT...ALLOWING SMOKE FROM FIREWORKS TO ACCUMULATE IN
URBAN AREAS. AN UPPER TROUGH WILL CONTINUE TO PROVIDE INSTABILITY
TONIGHT AND NEW YEARS DAY...BRINGING SHOWERY CONDITIONS WITH A
THREAT OF THUNDERSTORMS. TRADE WINDS WILL RETURN AFTER THE NEW
YEAR AS A HIGH PRESSURE STRENGTHENS NORTHEAST OF THE STATE.

&&

.DISCUSSION...
LIGHT WINDS AND AN UNSTABLE ATMOSPHERE REMAIN OVER THE STATE
TONIGHT WITH A WEAK SURFACE RIDGE TO THE NORTH AND AN UPPER LEVEL
TROUGH OVERHEAD. AS OF 730 PM...RAINFALL HAS DIMINISHED OVER OAHU
WHILE RAINFALL HAS PICKED UP OVER MOLOKAI...AND CONTINUED OVER
EASTERN MAUI AND THE WINDWARD BIG ISLAND. RADAR SHOWS SHOWERS
SOUTH OF OAHU AND MOLOKAI MOVING SLOWLY TOWARD THE NORTHEAST...AND
SHOWERS SOUTH AND WEST OF KAUAI MOVING NORTH. THESE SHOWERS AS
WELL AS SHOWERS FORMING OVER THE ISLANDS WILL AFFECT THE STATE
THROUGH THE NIGHT. THERE IS ALSO THE POSSIBILITY OF ISOLATED
THUNDERSTORMS WITH THE UPPER TROUGH PROVIDING THE INSTABILITY.

A SURFACE TROUGH 300 MILES WEST OF KAUAI HAS CREATED A LIGHT SOUTHEAST
FLOW AROUND THE STATE. THE LIGHT WINDS WILL ALLOW SMOKE FROM
FIREWORKS TO ACCUMULATE IN AND AROUND URBAN AREAS TONIGHT. SHOWERS
MAY ALLEVIATE SOME OF THE SMOKE BUILDUP...DEPENDING ON TIMING AND
LOCATION OF THE SHOWERS.

THE SURFACE TROUGH IS ALSO SUPPORTING A LINE OF THUNDERSTORMS JUST
OVER 100 MILES WEST OF KAUAI. THIS AREA OF THUNDERSTORMS HAS BEEN
MOVING SLOWLY EAST OVER THE PAST 6 HOURS BUT IS EXPECTED TO STALL
WEST OF KAUAI AND MOVE AWAY FROM THE STATE TOWARD THE WEST LATE
TONIGHT.

THE WINTER WEATHER ADVISORY REMAINS IN PLACE FOR THE BIG ISLAND
SUMMITS. THE CONVECTIVE NATURE OF THE PRECIPITATION WILL BRING A
HIGH VARIABILITY TO SNOW AMOUNTS...ESPECIALLY IF ANY THUNDERSTORMS
MOVE OVER THE SUMMIT.

LIGHT TRADE WINDS RETURN NEW YEAR DAY AS THE SUBTROPICAL RIDGE
REBUILDS TO THE NORTH. INSTABILITY REMAINS HIGH THURSDAY...SO
SHOWERS WITH LOCALLY HEAVY RAIN AND A CHANCE OF THUNDERSTORMS
REMAINS IN THE FORECAST THROUGH THURSDAY NIGHT. BY FRIDAY...THE
AIRMASS STABILIZES WITH A MORE TYPICAL TRADE WIND SHOWER PATTERN
EXPECTED. THE TRADES WILL FRESHEN OVER THE WEEKEND WITH GUSTY
CONDITIONS EXPECTED. RAINFALL WILL RETURN TO MAINLY WINDWARD AND
MAUKA LOCATIONS OVER THE WEEKEND.

THE MODELS SHOW SOME WEAKENING OF THE TRADE WINDS EARLY NEXT WEEK
WITH A COLD FRONT APPROACHING THE ISLANDS FROM THE NORTHWEST.

&&

.MARINE...
MODERATE WEST NORTHWEST SWELL CONTINUES WITH SURF HEIGHTS REACHING
ADVISORY LEVELS ON NORTH AND WEST FACING SHORES OF KAUAI AND NIIHAU
AND THE WEST FACING SHORES OF THE BIG ISLAND. THIS SWELL WILL
CONTINUE THROUGH THURSDAY...THEN GRADUALLY BECOME MORE NORTHWEST
AND DECREASE BELOW ADVISORY LEVELS BY FRIDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THURSDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-KONA-KOHALA.

WINTER WEATHER ADVISORY UNTIL 6 AM HST THURSDAY FOR BIG ISLAND
SUMMITS.

&&

MORRISON